To Plan B or To Not Plan B?

So my husband and I had sex last night. We never use condoms and always pull out. Doctors say I have horrible cysts and possible endometriosis so they tell me not to be too concerned about getting pregnant because it could be really hard. Plus it wouldn’t be the end of the world if we had a baby, because we both want kids and we are financially stable enough to do so. Well last night my husband accidentally ejaculated inside of me. This has happened before and we weren’t concerned because I was so close to my period. Everything ended up just fine. Well this time according to eve, it is my fertile week. So I am trying to decide if I should just take the plan B or just wait it out and see what happens. I have been told that plan B can make cysts and endo worse, or cause flare ups. Any advice on what I should do?